Shielded cable

ABSTRACT

In an electric power cable a neutral conductor comprising a plurality of separated wires is applied helically over an electrically conducting cable jacket in which longitudinal wires are embedded. The longitudinal wires serve to distribute any heavy fault currents among all the overlaid helical wires.

United States Patent I 1131 3,707,595

21 7 Appl. No.: 145,356 a [56] References Cited Plate v 2 v 1 1 Dec. 26,1972 54] SHIELDED CABLE 2 3,355,544 11 1967 Costley et al. ..174 106 R 73,351,706 11/1967 Gnerre etal .,..174 105R I 'J' 2,446,387 8/1948Peterson ..174/105 sc [73] Assignee: Anaconda Wire and Cable Company1,956,639 5/1934 Dana et'al ..174/106 30 2,337,556 12 1943 HOSkiilg174/106 sc Flledl M 20, 1971 v H 2,140,270 12/1938 Potter... ..174/115 xPrimary Examiner-Hemard A. Gilheany 52 -U.s.c1. 174/11s, 174/105'sc,174/120 sc Gnmley [51] Int 01b 9/02 An0rney-Victor F. Volk g5C8] Fieldof Search ..174/102 R, 102 SC,-' 105 R, 105 ABSTRACT 106 106 1 51 R SCin an electric power cable a neutral conductor comf prising a pluralityof separated wires is applied helically over an electrically conductingcable jacket in which longitudinal wires are embedded. The longitu-UNITED' STATES PATENTS dinal wires serve to distribute any heavy faultcurrents 3,474,189 10/1969 Plate et al ..174/115' among all the overlaidhelical wires. 2,258,687 10/1941 Peterson v ...174/l l5 1 3,571,6133/1971 Plate et a1 ..1'74/115 8 Claims, 2 Drawing Figures 8 PQLYMERICSHEATH .IZINSULATION use-semcomoubnwe JACKET PATENTED nu: 26 I972 Fig,

POLYMERIC SHEATH SEMICONDUCTING N w T A L U S W Q INVENTOR.

W. J. PLATE y Ma-Mf y 1 SHIELDED CABLE BACKGROUND OF THE INVENTION Inmodern electrical distribution systems it is important that theshielding on primary distribution cables be capable of carrying all thecurrent that is generated during fault conditions. The shielding systemmust keep within the temperature rating of the cable and, to ascurrentrequirements, and there are cases where the I shield must be equivalentto a No. 2 AWG (American Wire Gage) copper conductor. It is known-toform a neutral conductor or shield by winding a plurality of wires inparallel over a cable jacket. A typical example of a helical shieldequivalent to a No. 2 AWG copper wire would be 26 No. 16 AWG parallelhelical wires. A serious defect in such known shields results from thelikelihood that the fault current will be distributed among only a fewof the helical wires with a resulting burn-off and relaying malfunction.It has been sug gested to wrap a copper tape over the wires to connectthem to each other. This expedient would, however,.be expensive initself and the fragility of the tape might necessitate the additionalexpense of a protective sheath over the shielding. It has also beensuggested to apply half the shield wires with a left-hand lay and halfwith a right-hand lay, so that all the wires are interconnected,electrically. With this construction, however, the outer wires slip onthe inner helix and do not retain their even separation. They may evenbunch up and increase the cable diameter so that an assembly requiresmore than its alloted share of conduit space.

SUMMARY 1 have invented an electric power cable comprising apower-current carrying conductor, a layer of electrical insulationsurrounding the conductor, a semiconducting polymeric jacket surroundingthe insulation, a first plurality of circumferentially spaced,longitudinal wires embedded in the jacket, preferably with their outsidesurfaces tangent to the outer circumference of the jacket, and a second,greater plurality of wires wound helically directly over the jacket. Thehelical wires are separated from each other but the longitudinal wiresinterconnect them during a fault. The embedded wires may advantageouslybe undulatory as disclosed in U.S. Pat. No. 3,474,189 and/or the cablemay have longitudinal bosses as disclosed in U.S. Pat. No. 3,571,613.

BRIEF DESCRIPTION OF THE APPENDED DRAWING FIG. l shows a pictorial viewof a cable of my invenducting polymeric strand shielding, not separatelyshown. The conductor 11 is surrounded by a layer 12 of insulation suchas polyethylene, ethylene-propylene copolymer, or other dielectricextrudable material of which a number of suitable compositions areknown. In intimate contact with the layer 12, I have extruded a jacket13 of semiconducting polymeric material such as, but not limited to thematerial disclosed in U.S. Pat. Nos. 3,474,189 and 3,571,613. Six drainwires 14 are embedded in the jacket 13 with their outer surfaces tangentto the surface of the jacket layer. The drain wires 14 are not helicallywrapped around the cable, but extend longitudinally in parallel linesthat are equally spaced around the cable circumference. The number ofthe drain wires 14 will depend on the cable diameter, a larger number ofwires being used for the larger cables. I prefer, however, that thereshould be no fewer than three nor more than 12 embedded longitudinaldrain wires to obtain the maximum advantage from the present invention.Around the jacket 13 I have helically wound 18 shield wires 16. Theseare evenly spaced and separated from each other by gaps 17, with theresult that the wires 16 have a very long lay. A long lay is anadvantage in helical shield wires because of the lower current path andconsequently reduced resistance. The entire cable 10 is covered with anextruded polyethylene sheath 18 but this sheath will generally not berequired where copper is used for the wires 16. Other materials, such,for two examples, polyvinyl chloride and neoprene are suitable for thesheath 18. FIG. 2 shows a section of a cable similar to that of FIG. 1except that, instead of the smooth jacket 13 l have extruded a bossedjacket 19 with six radial bosses 21, containing the drain wires 14.

A detailed construction of an underground urban distribution (URD) cablemade to my invention is described in the example.

EXAMPLE conductor: mcm 61/wire aluminum, compacted strand shield:extruded semiconducting polymer insulation: cross-linked polyethylene,0.175 inch wall, diameter 1.46 inch jacket: semiconducting chlorinatedpolyethylene 0.100 inch wall, diameter 1.67 inch drain wires: 6 No. 15AWG solid bare soft copper, corrugated, embedded in jacket neutralconductor shield wires: 18 No. 16 AWG solid bare copper separator overshield: polyester tape sheath: high-molecular-weight polyethylene 0.080inch wall diameter 1.95 inch I have invented a new and useful electriccable of which the foregoing description has been exemplary rather thandefinitive and for which I desire an award of Letters Patentas definedin the appended claims.

I claim:

1. An electric power cable comprising:

A. a power-current carrying metallic conductor;

B. a layer of electrical insulation surrounding said conductor;

C. a semiconducting polymeric said insulation;

D. a first plurality of circumferentially spaced, longitudinal wiresembedded in said jacket; and

E. a second plurality, exceeding said first plurality, of

wires wound helically directly over said jacket,

jacket surrounding 3 4 said helically wound wires being separated from5. The cable of claim 2 wherein the outside surfaces each Other saidlongitudinal i es ele rically nv of said longitudinal wires aresubstantially tangent to terconnecting said helically wound wires duringth t r cir umference of said jacket. u 6. The cable of claim 1comprising an overall 2. The cable of claim I wherein said embeddedwires 5 are undulatory.

3; The cable of claim 1 comprising longitudinal bosses in said jacket. Y

4. The cable of claim 1 wherein the outside surfaces of saidlongitudinal wires are substantially tangent to the outer circumferenceof said jacket.

polymeric sheath.

7. The cable of claim 2 comprising an overall polymeric sheath.

8. The cable 'of claim 3 comprising an overall polymeric sheath.

3,707,595 December 26, 1972 Patent .No. Dated Walter J. PlateInventor(s) It is certified that error appears in the above-identifiedpatent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 64 after "spaced" and before the comma insert from eachother line 67 before "second" insert 1 neutral conductor comprising aSigned and sealed this 29th day of May 1973.

(SEAL) Attest! EDWARD M.FLETCHER,JR. ROBERT GOTT SCHALK AttestingOfficer Commissioner of Patents FORM PO-1 050 (10-69) USCOMM-DC6O376-P69 u.s. GOVERNMENT rnnmua OFFICE Isis mass-3:4.

CERTIFICATE OF CORRECTION 3 ,707 ,595 December 26, 1972 Patent No. DatedWalter J. Plate Inventor(s) It is certified that error appears in theab0veidentified patent and that said Letters Patent are hereby correctedas shown below:

Column 2, line 64 after "spaced" and before the comma insert es fromeach other line 67 before "second" insert 1 neutral conductor comprisinga Signed and sealed this 29th day of May 1973.

(SEAL) Attest! EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents FORM pomso ($69) uscoMM-oc 6037G-P69 .5.GOVERNMENT PRINTING OFFICE 2 l 0365'33.

2. The cable of claim 1 wherein said embedded wires are undulatory. 3.The cable of claim 1 comprising longitudinal bosses in said jacket. 4.The cable of claim 1 wherein the outside surfaces of said longitudinalwires are substantially tangent to the outer circumference of saidjacket.
 5. The cable of claim 2 wherein the outside surfaces of saidlongitudinal wires are substantially tangent to the outer circumferenceof said jacket.
 6. The cable of claIm 1 comprising an overall polymericsheath.
 7. The cable of claim 2 comprising an overall polymeric sheath.8. The cable of claim 3 comprising an overall polymeric sheath.